When you factor in the depth of the actual Apple Cinema, the viewing plane of the display ranges from about 6 inches from the back of the mount out to about 47 inches.  The image to the immediate left illustrates the arm without the Apple bracket and display.

The CDA4229 Apple Cinema arm has an available 28 inches of vertical travel. When the arm is wall mounted or mounted so that the lower part of the arm does not run into obstructions, full vertical range is possible.

When attached to a surface that impedes the vertical travel, the arm behaves as illustrated in the section below.

Use the CDA4229 without an extension for virtually all seated Cinema Display viewing applications.

Desk-edge clamp allows up to 18 inches of vertical travel. The standard CDA4229 provides plenty of height adjustability for virtually any requirement for seated desk height use and most standing applications.The lowest position possible position for this arm is 9.5 inches.

Desk edge mount with 5 inch extension allows up to 29.5 inches of vertical travel.

The CDA4229 5 inch extension provides more vertical travel when the arm is desk mounted. The bottom of the Cinema display may rest on the surface or be elevated up to 22 inches above the surface. This kind of vertical travel ensures that most people under 6' 6" tall will be comfortable either sitting or standing when the arm is attached to a desk that is around 29" tall.

Wall-mounted options allow for the full 29.5 inches of vertical travel of the CDA4229 Apple Cinema Display Arm.